The present disclosure relates, in various exemplary embodiments, to high temperature applications for bichromal balls and related signage or displays utilizing the same. The disclosure finds particular application in conjunction with reusable display technology and “electric paper,” which is electronically writeable and erasable and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiments are amenable to other like applications.
Bichromal balls, or beads as sometimes referred to in the art, are tiny spherical balls, such as micron-sized wax beads, which have an optical and an electrical anisotropy. These characteristics generally result from each hemisphere surface or side having a different color, such as black on one side and white on the other, and electrical charge, i.e., positive or negative. Depending on the electrical field produced, the orientation of these beads will change, showing a different color (such as black or white) and collectively create a visual image.
In this regard, the spherical particles are generally embedded in a solid substrate with a slight space between each ball. The substrate is then filled with a liquid (such as an oil) so that the balls are free to rotate in a changing electrical field, but can not migrate from one location to another. If one hemisphere is black and the other is white. Each pixel can be turned on and off by the electrical field applied to that location. Furthermore, each pixel can be individually addressed, and a full page image can thus be generated.
For example, reusable signage or displays can be produced by incorporating the tiny bichromal beads in a substrate such as sandwiched between thin sheets of a flexible elastomer and suspended in an emulsion. The beads reside in their own cavities within the flexible sheets of material. Under the influence of a voltage applied to the surface, the beads will rotate to present one side or the other to the viewer to create an image. The image stays in place until a new voltage pattern is applied using software, which erases the previous image and generates a new one. This results in a reusable signage or display that is electronically writable and erasable.
Furthermore, electronic displays produced by these bichromal balls or beads are sometimes referred to as “gyricon” displays. This terminology is reportedly the result of a combination of the Greek word for “rotating” and the Latin word for “image.”
Numerous patents describe bichromal balls, their manufacture, incorporation in display systems or substrates, and related uses and applications. Exemplary patents include, but are not limited to: U.S. Pat. Nos. 5,262,098; 5,344,594; 5,604,027 reissued as Re 37,085; 5,708,525; 5,717,514; 5,739,801; 5,754,332; 5,815,306; 5,900,192; 5,976,428; 6,054,071; 5,989,629; 6,235,395; 6,419,982; 6,235,395; 6,419,982; 6,445,490; and 6,703,074; all of which are hereby incorporated by reference. In addition, disclosure is provided by U.S. Pat. Nos. 4,126,854; and 5,825,529; and N. K. Sheridon et al., “The Gyricon—A twisting ball display”, Proc. SID, Boston, Mass., 289, 1977; T. Pham et al., “Electro-optical characteristics of the Gyricon display”, SID '02 Digest, 199, 2002; which again are hereby incorporated by reference.
Gyricon displays, or those based upon bichromal balls, are mainly used for indoor electronic signage applications. Outdoor applications are limited because the base polymer used in Gyricon media is a nonfunctional polyethylene, such as POLYWAX® 1000 or POLYWAX® 2000 from Baker Petrolite Corporation, Sugarland, Tex. The reason for the limited application is that at higher temperatures, it is believed that a fraction of the POLYWAX® leaches out to silicone fluid typically utilized inside the device, such as at about 50° C. to about 60° C. These unwanted materials are then carried or dispersed in the silicone fluid, thereby hindering bead rotation. As a result, the optical performances of the devices are significantly reduced. At present, the application temperature must generally be maintained below about 40° C. by various cooling methods and there is no very successful method to prevent the noted leaching difficulties described generally above.
Accordingly, there is a need for a bichromal ball display and related techniques for producing the same, that can be used at relatively high temperatures, and which avoids the problems associated with currently known displays.